1. Field of the Invention
The present invention relates to a metal catalyst and a fuel cell using an electrode that includes the catalyst. In particular, a metal catalyst has an improved catalytic efficiency in an electrochemical reaction and has a structure that promotes the permeation of gaseous reactants. A fuel cell that uses an electrode that includes the catalyst has improved efficiency.
2. Description of the Background
Fuel cells are emerging as a future source of clean energy that can replace fossil fuels.
The fuel cell is a power generating system that produces direct current by an electrochemical reaction between hydrogen and oxygen. A fuel cell includes a membrane electrode assembly (MEA) that has an electrolyte interposed between an anode and a cathode, and flow field plates for transferring gases. The electrodes include catalyst layers that are formed on supporting layers made of carbon paper or carbon cloth. However, it is difficult for gaseous reactants to reach the catalysts in the catalyst layer, and protons produced by the electrochemical reaction do not move rapidly. Thus catalysts have not been used effectively in electrodes.
The cathode and the anode are prepared by casting a slurry including a catalyst and an ionomer on a gas diffusion layer as a supporting layer, and drying the resultant to form a catalyst layer.
When the catalyst layer of an electrode is prepared in this way, the ionomer is doped in the catalyst or is simply mixed with the catalyst, which degrades the dispersion properties of the catalyst and causes agglomeration of the catalyst and the ionomer in the catalyst layer. As a result, an increase in the amount of unreacted catalyst due to secondary pores and non-uniform ionomers causes a reduction of catalyst utilization, a lack of fuel supply paths, and a reduction of the permeability of fuel, thereby significantly reducing the performance of the fuel cell. In addition, it is difficult to form and control a three-phase interface for an electrochemical reaction, and the catalytic efficiency is reduced.
FIG. 1B illustrates the structure of a conventional metal catalyst.
Referring to FIG. 1B, in a conventional metal catalyst 10, Pt particles 13 are present on the surface of the carbon 11, and PBI 12 is close to the carbon 11. In this structure, the dispersion properties of PBI and Pt/C deteriorate, and it is difficult to obtain a three-phase interface for an electrochemical reaction, and thus the catalytic efficiency is reduced.